The present invention relates to the manufacture of cellulose products made by the viscose process and other systems where spinnerets or casting nozzles are required. More particularly, this invention relates to an improvement in the spinning of viscose fibers.
It is very desirable both economically and from quality considerations to create a continuous viscose process from the start of pulp preparation to the final fiber.
The spinning machine itself should be continuous, especially for staple fiber. In fact a staple fiber spinning machine is continuous in concept and design. However, a factor infrequent in the chemistry of the process forces frequent discontinuities which are costly both directly and indirectly. Due to the forced interuptions, the spinning machine is, at best, a psuedocontinuous machine.
The discontinuity commonly occurs at the spinning jet. A rare metal jet through which viscose is extruded and then coagulated into fiber by the acid spinning bath, would not appear to be a cause of process interuption. In spinning alkali-cellulose-xanthate is broken down to cellulose and numerous by-products. Some of the by-products, in particular, various forms of free sulfur and the sulfide ion lead to a great deal of trouble at the jet.
The sulfide ion is the primary cause of trouble. It reacts with the zinc ion which occurs in virtually all modern spinning baths, and probably with the small amount of iron and calcium that appear as trace impurities in the bath. These metallic sulfides form a matrix around and within the individual jet capillaries.
Free sulfur "mud" and cellulose gels adhere to the frame work of the metallic sulfide matrix. As a result the jet capillaries become gradually choked off leading to various degrees of poor quality spinning before the trouble is detected. Eventually the plugging reaches a point where the spinning end breaks down or becomes obviously productively inferior short of shut down so that the end is pulled and the jet removed.
In some types of spinning the jet build-up is such that 100% jet change is required per 24 hours, and from 5-15% change per 24 hours is considered satisfactory.
This state of affairs leads to many undesirable results. That is,
(1) Spinning machines must be "overbuilt" since a substantial fraction of ends are effectively out of service at all times.
(2) Substantial quantities of viscose are lost by pulling bad jets and flushing new ones.
(3) Defective product.
(4) Labor expense in pulling, clearing, and replacing jets.
(5) Waste disposal problems of viscose waste at each change.
If a process or device were capable of eliminating the source of jet build up, the spinning process could become truly continuous for each individual spinning end.